Continuous Packet Connectivity (CPC), introduced in Release 7 of the 3rd-Generation Partnership Project (3GPP) specifications for the Universal Mobile Telecommunications System (UMTS), aims to improve the user experience by increasing battery lifetime. CPC also serves to increase network capacity, by reducing interference.
CPC is actually a collection of several features. First, CPC includes support for discontinuous transmission in the uplink (UL-DTX). This features enables the mobile station (user equipment, or UE, in 3GPP terminology) to transmit discontinuously on the uplink control channel (Uplink Dedicated Physical Control Channel, or U-DPCCH) during periods of inactivity, i.e., when the UE has no data to send. This saves battery power, since the UE can turn off transmitter circuitry, and also reduces interference, allowing for system capacity improvements. Second, CPC includes support for discontinuous reception of downlink transmissions (DL-DRX), which enables the UE to monitor the downlink control channel (High-Speed Shared Control Channel, or HS-SCCH) intermittently and thus also reduces batter power consumption in the UE. Third, CPC adds a new slot format in the uplink control channel (U-DPCCH), to improve power control of the downlink.
CPC operation is supported by a feature called “HS-SCCH Orders,” which provides a fast, layer 1 (L1) signaling mechanism for activating or deactivating uplink discontinuous transmission (UL-DTX) and/or downlink discontinuous reception (DL-DRX). These activation or deactivation orders are sent by a serving base station to the mobile terminal by sending layer 1 (L1) signaling commands to the UE on the High-Speed Shared Control Channel (HS-SCCH), without any involvement of the radio network controller (RNC).
Radio Resource Control (RRC) signaling is used to configure the behavior of the UE with respect to UL-DTX and DL-DRX. More particularly, RRC configuration sets several timing parameters that are applied by the UE to determine how often and when the UE should transmit on the uplink control channel and how often and when the UE should monitor the HS-SCCH.
CPC was first introduced in Release 7 of the 3GPP specifications and has been in use ever since. However, it has recently been recognized that the behavior of UEs designed to the Release 7 and Release 8 versions of the 3GPP specifications is not completely defined with respect to reconfiguration of UL-DTX and DL-DRX. More particularly, if a UE is already configured with DTX/DRX and receives a RRC reconfiguration message in which the value of the information element (IE) “DTX-DRX timing information” is not set to “Continue,” and if the serving High-Speed Downlink Shared Channel (HS-DSCH) cell was not changed as a result of this message, the UE's behavior with respect to “remembering” its CPC activation status is not clearly defined. The original intention behind the CPC specifications was that the UE remember the CPC activation status. Thus, if CPC was activated prior to the reconfiguration, CPC would continue to be activated subsequently to the RRC reconfiguration. Likewise, if CPC was not activated prior to the reconfiguration, it would remain that way afterwards. However, depending on a particular UE's implementation, it may or may not be designed to instruct the physical layer to consider that the DTX/DRX-related HS-SCCH orders received before the reconfiguration were never received. In other words, some Release 7 and Release 8 UEs may forget the CPC activation status as a consequence of the RRC reconfiguration described above. This will result in a mismatch between the serving base station (a “Node B,” in 3GPP terminology) and the UE regarding the CPC activation status. One example of a RRC configuration for which this mismatch would occur is during soft handover and softer handover when new DTX-DRX timing information is given to the UE via the RRC active set update message.
If the base station and the UE are mismatched with respect to CPC activation status, downlink messages to the UE can be missed, which will increase retransmissions and degrade user performance. Accordingly, techniques for avoiding or resolving these mismatches are needed.